﻿/************************************************************************

   Extended Silverlight Toolkit

   Copyright (C) 2010-2012 Xceed Software Inc.

   This program is provided to you under the terms of the Microsoft Public
   License (Ms-PL) as published at http://extendedsilverlight.codeplex.com/license

   Please purchase a commercial version of this toolkit if you are using
   it in a commercial product. The commercial versions support the project,
   and also include more features for each control, priority support,
   source code, updates, removed watermark, and a proprietary license.

   Visit http://xceed.com and follow @datagrid on Twitter.

  **********************************************************************/

using System;

namespace Xceed.Silverlight.DataGrid
{
  internal abstract class WeakViewModelBase : ViewModelBase
  {
    #region Constructor

    protected WeakViewModelBase()
    {
    }

    #endregion

    #region KeepAlive Property

    internal bool KeepAlive
    {
      get
      {
        return this.StayAlive();
      }
    }

    protected void RaiseKeepAliveChanged()
    {
      this.RaisePropertyChanged( () => this.KeepAlive );
    }

    #endregion

    #region Releasing Internal Event

    internal event EventHandler Releasing;

    protected virtual void OnReleasing()
    {
      this.RaiseReleasing();
    }

    private void RaiseReleasing()
    {
      if( this.Releasing != null )
      {
        this.Releasing( this, EventArgs.Empty );
      }
    }

    #endregion

    protected virtual bool StayAlive()
    {
      return false;
    }

    protected override void PreClear()
    {
      this.Release();

      base.PreClear();
    }

    protected override void OnClear()
    {
      this.Releasing = null;

      base.OnClear();
    }

    internal void Release()
    {
      this.OnReleasing();
    }
  }
}
